Why don't we see more things like:

All Random All Twin Ghosts
All Random All Warmogs
All Random All Rageblade
All Random All Phantom Dancers
All Random All Gunblades
All Random All Black Cleaver

We do have things like All Random All Warmogs, but on Summoner's Rift and not random.

Also because there's always that one guy who refuses to abide by the rules.

ARAGB

if the passive cooldown stacks, HOLY JEEBUS YES

gunshots going out every 5 seconds

All Random All Zeal was cool, but then the movement speed on Zeal/Phantom Dancer got nerfed.

Because stacking Phantom Dancers is hard after the attack speed nerfs.

Because Riot has not yet implemented redundant-champions-on-same-team yet; so we can't have
5v5 All Karthus
5v5 All Draven
5v5 All Teemo
5v5 All Singed
5v5 All Akali
5v5 All Xerath
10v0 All Mordekaiser...

i would kinda want to to see
All Random Same Hero
imagine the 5 man lux ults

kinda like how dota's SHOM works (same hero only mid)

im going to make an all warmongs game right now XD haha!!

All Statikk Shivs.